Method for providing nonvolatile storage write bandwidth using a caching namespace

ABSTRACT

An apparatus for implementing an enhanced-write-bandwidth caching stream includes a memory that stores machine instructions and a processor that executes the machine instructions. The apparatus receives a first host write stream and a second host write stream that comprises latency-sensitive host write requests. The apparatus also subjects the first host write stream to host-write throttling, and exempts the second host write stream from host-write throttling. The apparatus further requires that the second host write stream invalidate logical blocks in an order corresponding to a previous order in which the respective logical blocks were previously programmed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. patent application Ser. No. ______concurrently filed herewith, entitled METHOD FOR PROVIDING NONVOLATILESTORAGE WRITE BANDWIDTH USING A CACHING NAMESPACE, the entire disclosureof which is incorporated herein by reference.

TECHNICAL FIELD

This description relates generally to nonvolatile storage devices, andmore particularly to defining a logical cache reserve to provide writebandwidth in a nonvolatile storage device.

BACKGROUND

Nonvolatile storage devices are used as primary and secondary datastorage in computer systems. Some existing nonvolatile storage devicesimplement arrays of flash memory cells based on floating-gate transistortechnology, such as NAND flash memory cells, to store electronic data ina format that can persist without a continuous power supply. The datatypically consists of computer instructions, numerical data, applicationprograms, operating systems, and the like.

The implementation of certain types of nonvolatile storage devicesrequires that fixed-size sections, or blocks, of memory cells withpreviously-stored data be erased before being reprogrammed with newdata. Typically, the size of these blocks is larger than the size offixed-size sections, or pages, of memory cells that can be programmed.

The conventional process of moving valid data remaining in portions of ablock of memory cells before erasing the block and making the blockavailable for reprogramming, collectively referred to as garbagecollection, results in nonvolatile memory write operations that do notdirectly serve host (user) write requests. The total amount of datawritten in the nonvolatile memory over time—including host-request writeoperations, garbage collection write operations, and other storagedevice write operations—as a ratio to the amount of host (user) datawritten is known as write amplification.

Since the program/erase (P/E) lifecycle, or endurance, of typicalnonvolatile memory cells is limited, some existing nonvolatile storagedevices have implemented measures to extend the lifespan, or theperceived lifespan, of the nonvolatile storage devices. For example,typical nonvolatile storage devices present less total logical addressspace to hosts than the actual capacity of the memory cells in thedevice, known as over-provisioning. In addition, some nonvolatilestorage devices limit the quantity of host writes over time based on thecurrent amount of storage space available for programming orreprogramming, a practice known as throttling.

However, particular nonvolatile storage use cases can be relativelysensitive to write latency and require relatively high write performanceon an on-demand basis for relatively limited amounts of data. Forexample, limited-capacity, on-demand write bandwidth can be required tosave the main memory contents and processor state during the initiationof system hibernation mode. As a result, host-write throttling canhinder desired performance regarding certain use cases.

SUMMARY

According to one embodiment of the present invention, an apparatus forimplementing an enhanced-write-bandwidth caching stream includes amemory that stores machine instructions and a processor that executesthe machine instructions. The apparatus receives a first host writestream and a second host write stream that comprises latency-sensitivehost write requests, subjects the first host write stream to host-writethrottling, and exempts the second host write stream from host-writethrottling. The apparatus further requires that the second host writestream invalidate logical blocks in an order corresponding to a previousorder in which the respective logical blocks were previously programmed.

According to another embodiment of the present invention, an apparatusfor implementing an enhanced-write-bandwidth caching stream includes amemory that stores machine instructions and a processor that executesthe machine instructions. The apparatus divides a stream of host writerequests into a first host write stream and a second host write streamthat comprises latency-sensitive host write requests. The apparatusfurther invalidates logical blocks corresponding to the second hostwrite stream in an order corresponding to a previous order in which therespective logical blocks were previously programmed.

According to yet another embodiment of the present invention, acomputer-implemented method for implementing an enhanced-write-bandwidthcaching stream includes apportioning a first address space and a secondaddress space associated with a storage device, the second address spacecomprising a logical namespace. The method also includes subjecting thefirst address space to host-write throttling, and exempting the secondaddress space from host-write throttling. The method further includesrequiring that logical block addresses corresponding to the secondaddress space be invalidated in an order corresponding to a previousorder in which the respective logical blocks were previously programmed.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram depicting an exemplaryenhanced-write-bandwidth caching stream using anenhanced-write-bandwidth address space in accordance with an embodimentof the present invention.

FIG. 2 is a block diagram illustrating an exemplary storage device thatcan employ an enhanced-write-bandwidth address space to implement theenhanced-write-bandwidth caching stream of FIG. 1 in accordance with anembodiment of the present invention.

FIG. 3 is a block diagram illustrating an exemplary general computingsystem that can implement the host system of FIG. 1 in accordance withan embodiment of the present invention.

FIG. 4 is a process flowchart representing an exemplary method ofimplementing an enhanced-write-bandwidth storage caching stream inaccordance with an embodiment of the present invention.

FIG. 5 is a process flowchart representing another exemplary method ofimplementing an enhanced-write-bandwidth storage caching stream inaccordance with an embodiment of the present invention.

FIG. 6 is a process flowchart representing an exemplary method ofimplementing an enhanced-write-bandwidth host caching stream inaccordance with an embodiment of the present invention.

FIG. 7 is a process flowchart representing another exemplary method ofimplementing an enhanced-write-bandwidth host caching stream inaccordance with an embodiment of the present invention.

DETAILED DESCRIPTION

An embodiment of the present invention defines a reserved logicalnamespace for caching in a storage device. The caching namespace isexempted from host-write throttling with respect to stored data sets upto the size of the namespace, irrespective of other workloadssimultaneously being executed in other namespaces of the storage device.In general, host writes to the reserved namespace are not blocked bystorage device reclamation (garbage collection) activities. Thecorresponding host system is responsible for invalidating, ordeallocating, data in the caching namespace, for example, using a TRIMcommand, to indicate the storage area can be reclaimed in preparationthe next caching use of the namespace.

An embodiment of the present invention is shown in FIG. 1, whichillustrates an exemplary storage system 10 that employs anenhanced-write-bandwidth address space 12 in order to implement anenhanced-write-bandwidth caching stream 14. The storage system 10includes the enhanced-write-bandwidth address space 12, anenhanced-write-bandwidth available blockset pool 16, a general addressspace 18, a general available blockset pool 20, a general throttlingmechanism 22, a write stream aggregator 24, an enhanced throttlingmechanism 26 and a reclamation engine 28.

A host system 48 is communicatively connected to the storage system 10,for example, by way of a storage bus or a communication network, inorder to send host data to the storage system 10. Host write requests 46generated by the host system 48 associated with the storage system 10are divided into separate write data streams, including alatency-sensitive write stream 52 and a general host write stream 54 bya write request divider 56.

A buffered host write stream 30 feeds general host write requests 34into the general throttling mechanism 22, which generates areclamation-balanced host write stream 36. Storage devices thatimplement NAND flash memory conventionally attempt to approximatelybalance host write throughput with reclamation (garbage collection)activities that reclaim free space available for programming for futurewrite operations. Typical systems temporarily or intermittently reducehost-write throughput as needed to maintain relatively acceptablemaximum command response times and to allow reclamation activities tokeep up with ongoing host writes.

As known in the art, storage devices utilizing NAND flash memorytypically employ a logical construct consisting of multiple blocks ofmemory cells over which garbage collection activities are coordinated,for example, a blockset including an integer number of NAND blocks (alsoreferred to as erase blocks). The reclamation engine 28 generates areclamation write stream 38, which is combined with thereclamation-balanced host write stream 36 by the write stream aggregator24 to create an aggregate general write stream 42 that feeds into thegeneral available blockset pool 20 in the general address space 18. Inan alternative embodiment, the reclamation write stream 38 remainsindependent of the reclamation-balanced host write stream 36, which canhelp separate relatively dynamic, or “hot,” data from relatively static,or “cold,” data.

So long as the amount of programmable space available in the generalavailable blockset pool 20 remains above a predetermined throttlingthreshold 58, the general throttling mechanism 22 does not modify thethroughput of the reclamation-balanced host write stream 36, whichremains the same as that of the buffered host write stream 30. However,during periods when the programmable space available in the generalavailable blockset pool 20 drops below the throttling threshold 58, thegeneral throttling mechanism 22 reduces the throughput of thereclamation-balanced host write stream 36 from that of the buffered hostwrite stream 30 in order to afford increased prioritization toreclamation write requests and avoid free blockset starvation, which canbe perceived by the host as a quality of service disruption.

The enhanced-write-bandwidth address space 12 of the storage system 10generally is not subject to internal host write throttling, whichattempts to approximately equalize the host write throughput with therate of the ongoing reclamation process. While throttling generally isprovided with regard to the general host write stream 54, thelatency-sensitive write stream 52 generally is guaranteed the maximumrealizable throughput based on the available resources.

The buffered latency-sensitive write stream 32 feeds latency-sensitivewrite requests 44 into the enhanced throttling mechanism 26. Theenhanced-write-bandwidth caching stream 14 feeds latency-sensitive writerequests 44 from the enhanced throttling mechanism 26 into theenhanced-write-bandwidth available blockset pool 16 in theenhanced-write-bandwidth address space 12.

So long as programmable space is available in theenhanced-write-bandwidth available blockset pool 16, theenhanced-write-bandwidth caching stream 14 is not modified by theenhanced throttling mechanism 26. However, if theenhanced-write-bandwidth available blockset pool 16 does not have anyprogrammable space available, the throughput of theenhanced-write-bandwidth caching stream 14 is reduced by the enhancedthrottling mechanism 26 with respect to the throughput of the bufferedlatency-sensitive write stream 32.

The enhanced throttling mechanism 26 maintains a budgeted or apportionedgroup of clean data blocks, or blocksets, associated with a specialcaching namespace, the enhanced-write-bandwidth address space 12. Forexample, in an embodiment, the special caching namespace includes alogical block address (LBA) space defined by NVM Express (NVMe) or otherspecification for accessing storage devices attached through ahigh-speed serial computer expansion bus, such as a storage buscomplying with the Peripheral Component Interconnect Express (PCIe)standard. As known in the art, the PCIe/NVMe storage interface enableshost system creation, resizing and deletion of logical namespaces.

In general operation, other write streams, such as the general hostwrite steam 54, are unaware of the enhanced-write-bandwidth addressspace 12 and do not have access to the write-bandwidth-enhanced addressspace 12. Similarly, the general throttling mechanism 22 is unaware ofthe budgeted or apportioned group of clean data blocks, or blocksets,associated with the special caching namespace, orenhanced-write-bandwidth address space 12. As a result, in general,other write streams, including the general host write steam 54, arethrottled by the general throttling mechanism 22 earlier than thewrite-bandwidth-enhanced caching stream 14 is reduced by the enhancedthrottling mechanism 26.

In an alternative embodiment, the enhanced-write-bandwidth address space12 and the general address space 18 share a common available blocksetpool. In other words, the enhanced-write-bandwidth available blocksetpool 16 and the general available blockset pool 20 are consolidated, andboth the enhanced-write-bandwidth address space 12 and general addressspace 18 draw from the consolidated available blockset pool. In thiscase, the general throttling mechanism 22 is triggered by apredetermined consolidated throttling threshold regarding the totalamount of programmable space available in the consolidated pool.

For example, a parameter that is provided to the general throttlingmechanism 22 representing the number of data blocks, or blocksets,currently available for programming is reduced by the current amount ofcaching namespace, or enhanced-write-bandwidth address space 12, thatcurrently is available for programming. For example, the parameter“clean_blocksets” represents the number of blocksets currently availablefor programming in the storage system 10, and the modified parameter“adjusted_clean_blocksets,” defined as the number of blocksets currentlyavailable for programming in the storage system 10 reduced by thecaching capacity in the enhanced-write-bandwidth address space 12currently available for programming, is presented to the generalthrottling mechanism 22 according to the following equation:

adjusted_clean_blocksets=clean_blocksets−(caching_capacity−cached_data_written)

In this equation, “caching_capacity” is defined as the size (in units ofblocksets) of the caching namespace, or enhanced-write-bandwidth addressspace 12, without additional overprovisioning. Additionally,“cached_data_written” is the amount of data (in units of blocksets) thathas been written to the namespace.

In this example, the modified parameter “adjusted_clean_blocksets” isused by the general throttling mechanism 22 to determine if thethrottling threshold 58 is reached. If the current value of theparameter “adjusted_clean_blocksets” is below the level of thethrottling threshold 58, then the general throttling mechanism 22reduces the throughput of the reclamation-balanced host write stream 36,even though the total amount of storage space currently available forprogramming in the storage device 10, including available blocksetsassigned to the enhanced-write-bandwidth address space 12, is greaterthan the throttling threshold 58.

In an alternative embodiment, the host throttle metric has granularityfiner than the blockset size, and the alternative modified parameter“adjusted_free_apace” may be presented to the general throttlingmechanism 22 according to the following equation:

adjusted_free_space=free_space−(caching_capacity−cached_data_written)

Thus, in general, the enhanced-write-bandwidth address space 12 iscontinuously maintained as a reserved caching namespace for use bylatency-sensitive write requests 44 from the host system 48. Theenhanced-write-bandwidth caching stream 14 is reduced by the enhancedthrottling mechanism 26 only in the case that theenhanced-write-bandwidth address space 12 becomes full, that is, whenthere is no programmable space currently remaining in theenhanced-write-bandwidth address space 12. The enhanced-write-bandwidthcaching stream 14 effectively bypasses the enhanced throttling mechanism26 whenever “caching_capacity” is greater than “cached_data_written.”

In general, the host system 48 and the storage system 10 must maintainindependent flow with regard to the general stream and thelatency-sensitive, or enhanced, stream of write requests. Variousconfigurations and methods can be implemented to accomplish this goal.

In some embodiments, the host system 48 implements separate physicalstreams corresponding to the latency-sensitive write stream 52 and thegeneral host write stream 54, with independent buffering resourcesdedicated to the general host write requests 34 and thelatency-sensitive write requests 44. In this case, the buffers canoperate, for example, using a first-in-first-out (FIFO) method. Thus,the physical flow is implemented essentially as the conceptual flowillustrated in the host system 48 of FIG. 1.

In other embodiments, the host system 48 may be implemented using aphysical configuration that does not correspond to the conceptual flow,but nonetheless accomplishes essentially the same principle. Forexample, the latency-sensitive write stream 52 and the general hostwrite stream 54 may be implemented in a single physical stream, and thegeneral host write requests 34 and latency-sensitive write requests 44may be stored in a single queue from which the host system 48 has theability to selectively forward write requests in a different order thanthese enter the queue.

Similarly, in some embodiments the buffered host write stream 30 and thebuffered latency-sensitive write stream 32 are implemented in separatephysical streams, for example, independent storage buses orcommunication networks. In other embodiments, the buffered host writestream 30 and buffered latency-sensitive write stream 32 may bephysically implemented in a consolidated storage bus or communicationnetwork.

In an embodiment, the storage system 10 implements separate physicalresources for the general stream of write requests (including, forexample, the general throttling mechanism 22, the reclamation-balancedhost write stream 36 and the aggregate general write stream 42) versusthe latency-sensitive, or enhanced, stream of write requests (including,for example, the enhanced throttling mechanism 26 and theenhanced-write-bandwidth caching stream 14).

Other embodiments that share resources among the write streams whilemaintaining independent flows between the write streams may beimplemented. As an example, in some embodiments, the general throttlingmechanism 22 and the enhanced throttling mechanism 26 use sharedresources. As another example, one or more shared buffers may beimplemented from which the storage system 10 has the ability toselectively forward write requests in a different order than thesearrive.

In general, when “cached_data_written” is equal to “caching_capacity”the reserved space in the enhanced-write-bandwidth address space 12accounted for by “adjusted_clean_blocksets” is exhausted, and thecaching namespace is considered to be full. In this state, the writebandwidth generally reserved for the enhanced-write-bandwidth cachingstream 14 cannot be guaranteed, and the enhanced-write-bandwidth addressspace 12 behaves in the same manner as other namespaces in the storagesystem 10. That is, during periods when the data cached in the cachingnamespace reaches the capacity of the enhanced-write-bandwidth addressspace 12, the enhanced throttling mechanism 26 temporarily modifies thethroughput of the enhanced-write-bandwidth caching stream 14.

Data sets stored in the enhanced-write-bandwidth address space 12 can bedefined to have a lifecycle that includes an invalidation step thatindicates when the data no longer includes valid entries or entries thatare duplicated in a transfer buffer so that the storage space can bereclaimed. In an embodiment, a TRIM command is sent to the storagesystem 10 by the operating system of the host system 48 to indicateinvalid data in the enhanced-write-bandwidth address space 12.

The TRIM command informs the storage system 10 that the invalidated datais no longer useful and permits the reclamation engine 28 to reclaim thecorresponding storage space. The TRIM command reduces the value of“cached_data_written” by the quantity of data trimmed. If a host system48 subsequently attempts to read the invalidated data, the storagesystem 10 can return the obsolete data or a sequence of zeroes. Ingeneral, host purges can be invoked as background erasures as part ofthe storage system TRIM command processing routine.

In an embodiment, the garbage collection blockset selection algorithmutilized by the reclamation engine 28 operates asynchronously withrespect to the general throttling mechanism 22. However, the garbagecollection blockset selection algorithm must also use the“adjusted_clean_blocksets” parameter to ensure the reclamation engine 28operates whenever the host general throttling mechanism 22 engages.Otherwise, the garbage collection selection algorithm is unchanged fromconventional nonvolatile memory management systems known in the art.

It is desirable to guarantee, to the extent practicable, that thereclamation process operates at a faster rate than incoming host writes.Toward this end, it is desirable to provide embodiments that avoidgarbage collection overhead, that is, implementations that generally donot require resources to move valid data to other data blocks, orblocksets, before performing erasures. Such implementations ensure thatonly erasure of data blocks, or blocksets, (without relocation of validdata) in the enhanced-write-bandwidth address space 12 is requiredbefore reprogramming, permitting nearly instantaneous reuse of datablocks, or blocksets, in the enhanced-write-bandwidth address space 12.

In one such embodiment, the host system 48 is required to purge theenhanced-write-bandwidth address space 12 before the data cached in thecaching namespace reaches the capacity of the enhanced-write-bandwidthaddress space 12. The host system 48 is required to invalidate data inthe enhanced-write-bandwidth address space 12 after the data is nolonger useful, but no later than when the value of “cached_data_written”becomes equal to “caching_capacity” to ensure there is no garbagecollection overhead during the purge.

In this embodiment, the host system 48 is permitted to perform writerequests using any access pattern with respect to data blocks, orlogical block addresses. However, the host system 48 is not permitted towrite more than the number of LBAs equal to the size of theenhanced-write-bandwidth address space 12 before purging the cachingnamespace. Thus, the host system 48 must track the number of LBAswritten in the caching namespace since the last purge, and invalidateall valid data in memory cells pertaining to theenhanced-write-bandwidth address space 12 at an interval not exceedingthe number of host writes equaling the capacity of theenhanced-write-bandwidth address space 12.

For example, after writing enough LBAs to fill theenhanced-write-bandwidth address space 12, the host system 48 mayperform an explicit TRIM command with respect to all currently validLBAs pertaining to the caching namespace. Otherwise, in a simplifiedprocedure, the host system 48 may perform a TRIM command with respect tothe entire enhanced-write-bandwidth address space 12. This host systempurge requirement is important to sustain a desired or guaranteedperformance profile.

In another such embodiment, a restriction is placed upon the host system48 requiring that latency-sensitive write requests 44 invalidate datablocks or logical block addresses (LBAs) in the same order that thelogical block addresses were previously written. In this case, the hostsystem 48 is not required to perform explicit TRIM commands with respectto the caching namespace. In a simplified procedure, the host system 48may sequentially write and rewrite logical block addresses inlatency-sensitive write requests 44.

In this embodiment, the storage system 10 reserves one blockset ofoverprovisioned space, which is not visible to the host system 48. Thereserved blockset permits transition from a programmed state to anerased state while the caching namespace is at full capacity.

In effect, this implementation permits the host system 48 tocontinuously write to the caching namespace without throttling, becausein conventional storage systems, erase bandwidth is greater thanhost-write bandwidth. As a result, this write access pattern restrictionon the host system 48 virtually ensures that the reclamation processwill outperform arriving write requests, such that latency-sensitivewrite requests 44 will virtually never be delayed during normal systemoperation.

These implementations, including the requirements placed on the hostsystem 48, are intended to ensure that programmable space remainsavailable in the enhanced-write-bandwidth address space 12 during allnormal operating conditions. Effectively, the enhanced-write-bandwidthaddress space 12 is continuously maintained as a reserved cachingnamespace for use by latency-sensitive write requests 44 from the hostsystem 48.

In a further embodiment, the storage system 10 implements a verificationcheck to ascertain that the host system 48 obeys the write accesspattern restriction. If the storage system 10 determines the rule hasbeen violated, then the storage system 10 can temporarily operate theenhanced-write-bandwidth address space 12 in the same manner as thegeneral address space 18 until such time that the storage system 10 isable to verify host system compliance.

In some embodiments, additional write resources with respect toconventional systems are assigned to the enhanced-write-bandwidthcaching stream 14 to ensure reclamation activities and general hostwrite requests 34 that generally are subject to throttling do not blocklatency-sensitive write requests 44 directed to theenhanced-write-bandwidth address space 12. In an embodiment, dedicatedwrite resources are reserved in the storage device logic circuitry forthe enhanced-write-bandwidth caching stream 14. The required resourcesdepend on the storage device architecture and are specific to theparticular implementation.

In an alternative embodiment, the storage system 10 sends asynchronousnotifications to the host system 48 regarding theenhanced-write-bandwidth address space 12. For example, the storagesystem 10 may send a notification to the host system 48 indicating thatthe enhanced-write-bandwidth address space 12 is ready, or indicatingthe enhanced-write-bandwidth address space 12 is full.

Implementation of the enhanced-write-bandwidth address space 12 and theenhanced-write-bandwidth caching stream 14 can be applied to any storagesystem that utilizes reclamation (garbage collection) in order toprovide limited-capacity, on-demand write bandwidth for use inparticular nonvolatile storage use cases that are relatively sensitiveto write latency. Various embodiments can deliver relatively high writeperformance to host systems on an on-demand basis for relatively limitedamounts of data.

For example, the enhanced-write-bandwidth address space 12 can beutilized to save a write burst containing the host system memorycontents and processor state during the initiation of host systemhibernation mode, or to save logging information. Laptop computersgenerally enter hibernation mode by saving a data burst fromnon-persistent memory to nonvolatile memory. The data burst isrelatively latency-sensitive, because the time required to store thedata burst directly affects the hibernation time experienced by users.Upon power-up, the host system reads the data into memory. After thedata set has been read into memory, the data in the caching namespace isno longer useful and can be invalidated (trimmed).

The reservation of overprovisioned space in the storage system 10 foruse in the enhanced-write-bandwidth address space 12 results in atradeoff regarding write amplification and performance in the generaladdress space 18. However, the resulting effect is essentially minimizedin an embodiment where the enhanced-write-bandwidth address space 12 ismuch smaller than the total budgeted or apportioned overprovisionedspace in the storage system 10.

In an alternative embodiment, the special caching namespace includes alogical namespace associated with a logical unit number (LUN) defined bya serial-attached SCSI (SAS) standard. In another alternativeembodiment, the special caching namespace is defined as an LBA range inthe global (LUN 0) LBA space on the storage device. In general, thecaching namespace may be specified by the host and communicated to thestorage device in any manner known in the art.

In other alternative embodiments, multiple instances of cachingnamespaces, or enhanced-write-bandwidth address spaces, are reserved ina single storage system. In addition, in an embodiment, multipleinstances of caching namespaces are presented to the host system as asingle customer-visible namespace with customer-defined logical blockaddress boundaries.

As illustrated in FIG. 2, an exemplary storage device 60 that canimplement the enhanced-write-bandwidth caching stream 14 of FIG. 1, forexample, in conjunction with a host system, includes a controller 62, amemory 64, a host interface 66, and nonvolatile memory (NVM) 68. In anembodiment, the storage device 60 includes a NAND-flash basedsolid-state drive (SSD).

The controller 62 may include any general or application-specificdigital processor suitable for controlling a storage device. The memory64 may include any digital memory device suitable for storing data andinstructions for access by the controller 62. The host interface 66 mayinclude any networking interface suitable for communicatively connectingthe storage device 60 to a host system. The host interface 66 mayimplement a storage networking standard, for example, NVM Express (NVMe)or SAS (serial-attached Small Computer System Interface [SCSI]). Thenonvolatile memory 68 may include, for example, NAND flash memory chips,or any other suitable nonvolatile memory known in the art.

Programming code, such as source code, object code or executable code,stored on a computer-readable medium, including firmware, can beexecuted by the controller 62 in order to perform the functions of theenhanced-write-bandwidth caching stream 14 of FIG. 1.

As illustrated in FIG. 3, an exemplary general computing device 70 thatcan be employed as a host system 48 to implement theenhanced-write-bandwidth caching stream 14 of FIG. 1, for example, inconjunction with a storage device, includes a processor 72, a memory 74,an input/output device (I/O) 76, a display device 78, a storage 80 and anetwork interface 82. The various components of the computing device 70are coupled by a local data link 84, which in various embodimentsincorporates, for example, an address bus, a data bus, a serial bus, aparallel bus, or any combination of these.

In various embodiments, the computing device 70 can include, forexample, a server, a controller, a workstation, a mainframe computer,personal computer (PC), a computing tablet, a personal digital assistant(PDA), a smart phone, a wearable device, or the like. Programming code,such as source code, object code or executable code, stored on acomputer-readable medium, such as the storage 80 or a peripheral storagecomponent coupled to the computing device 70, can be loaded into thememory 74 and executed by the processor 72 in order to perform thefunctions of the host system 10.

Referring now to FIG. 4, an exemplary process flow is illustrated thatmay be performed, for example, by the storage system 10 of FIG. 1 toimplement an embodiment of the method described in this disclosure foremploying an enhanced-write-bandwidth address space in order toimplement an enhanced-write-bandwidth caching stream. The process beginsat block 92, where a general host write stream is received, as describedabove.

In block 94, the amount of available space of memory cells currentlyavailable for programming in the general address space is determined, asexplained above. For example, the number of blocksets available forprogramming in the caching namespace, or enhanced-write-bandwidthaddress space, is subtracted from the total number of blocksetsavailable for programming in both the general address space and thecaching namespace.

In block 96, the amount of available space in the general address spaceis compared to a predetermined threshold, as described above. If thecurrent available space in the general address space is greater than orequal to the threshold, then the general write stream is permittedunthrottled throughput in block 98 and the enhanced-write bandwidthcaching stream is permitted unthrottled throughput in block 100.

Otherwise, if the current available space is less than the threshold,then the general write stream is reduced, or throttled, in block 102 toapproximately balance the general write stream with the reclamationrate, as explained above. In any case, regardless of the available spacein the general address space, the enhanced-write bandwidth cachingstream is permitted unthrottled throughput in block 104.

As described above, in block 106, the general write stream is combinedwith the reclamation write stream to create an aggregate write stream,which is stored in the general address space in block 108.

Referring to FIG. 5, another exemplary process flow is illustrated thatmay be performed by the storage system 10 of FIG. 1, for example, inconjunction with the process flow of FIG. 4, to implement an embodimentof the method described in this disclosure for employing anenhanced-write-bandwidth address space in order to implement anenhanced-write-bandwidth caching stream. The process begins at block112, where a caching namespace, or enhanced-write-bandwidth addressspace, is reserved apart from the general address space at the requestof the host, as explained above.

In block 114, a latency-sensitive host write stream is received, asdescribed above. In block 116, the amount of available space of memorycells currently available for programming in the caching namespace isdetermined, as explained above. If the available space in the cachingnamespace is greater than zero, in block 118, then theenhanced-write-bandwidth caching stream is permitted unthrottledthroughput in block 120.

Otherwise, if the available space in the caching namespace equals zeroin block 118, then the throughput of the enhanced-write-bandwidthcaching stream is reduced, or throttled, in block 122, as furtherexplained above. In block 124, the enhanced-write-bandwidth cachingstream is stored in the caching namespace, as described above.

Referring to FIG. 6, an exemplary process flow is illustrated that maybe performed by the host system 48 of FIG. 1, for example, inconjunction with the process flows of FIGS. 4 and 5, to implement anembodiment of the method described in this disclosure for employing anenhanced-write-bandwidth address space in order to implement anenhanced-write-bandwidth caching stream. The process begins at block130, where the caching namespace is defined, as explained above. Forexample, the host specifies a logical namespace in accordance with theNVMe standard.

In block 132, the host generates write requests, and in block 134, thehost write requests are divided, or separated, into latency-sensitivewrite requests and general write requests, as described above. In block136 the general write requests are sent, for example, to a storagedevice. A number of latency-sensitive write requests sufficient to equalthe size of the caching namespace are sent, for example, to the storagedevice, in block 138. As explained above, a TRIM command is sent withrespect to currently valid logical block addresses (LBAs) correspondingto the latency-sensitive write requests, in block 140.

Referring to FIG. 7, an exemplary process flow is illustrated that maybe performed by the host system 48 of FIG. 1, for example, inconjunction with the process flows of FIGS. 4 and 5, to implement anembodiment of the method described in this disclosure for employing anenhanced-write-bandwidth address space in order to implement anenhanced-write-bandwidth caching stream. The process begins at block142, where the caching namespace is defined, as explained above.

In block 144, additional overprovisioned space, for example, oneadditional blockset, is reserved to allow erasure transition whilecaching namespace is at capacity, as explained above. In block 146, thehost generates write requests, and in block 148, the host write requestsare divided, or separated, into latency-sensitive write requests andgeneral write requests, as described above.

In block 150 the general write requests are sent, for example, to astorage device. Latency-sensitive write requests also are sent, forexample, to the storage device, in block 152. As explained above,logical block addresses (LBAs) corresponding to the latency-sensitivewrite requests are invalidated, in block 154, in the same order that therespective LBAs were previously written.

Aspects of this disclosure are described herein with reference toflowchart illustrations or block diagrams, in which each block or anycombination of blocks can be implemented by computer programinstructions. The instructions may be provided to a processor of ageneral purpose computer, special purpose computer, or otherprogrammable data processing apparatus to effectuate a machine orarticle of manufacture, and when executed by the processor theinstructions create means for implementing the functions, acts or eventsspecified in each block or combination of blocks in the diagrams.

In this regard, each block in the flowchart or block diagrams maycorrespond to a module, segment, or portion of code that including oneor more executable instructions for implementing the specified logicalfunction(s). It should also be noted that, in some alternativeimplementations, the functionality associated with any block may occurout of the order noted in the figures. For example, two blocks shown insuccession may, in fact, be executed substantially concurrently, orblocks may sometimes be executed in reverse order.

A person of ordinary skill in the art will appreciate that aspects ofthis disclosure may be embodied as a device, system, method or computerprogram product. Accordingly, aspects of this disclosure, generallyreferred to herein as circuits, modules, components or systems, may beembodied in hardware, in software (including firmware, residentsoftware, micro-code, etc.), or in any combination of software andhardware, including computer program products embodied in acomputer-readable medium having computer-readable program code embodiedthereon.

It will be understood that various modifications may be made. Forexample, useful results still could be achieved if steps of thedisclosed techniques were performed in a different order, and/or ifcomponents in the disclosed systems were combined in a different mannerand/or replaced or supplemented by other components. Accordingly, otherimplementations are within the scope of the following claims.

1. An apparatus for implementing an enhanced-write-bandwidth caching stream, the apparatus comprising: a memory that stores machine instructions; and a processor that executes the machine instructions to receive a first host write stream and a second host write stream comprising latency-sensitive host write requests, subject the first host write stream to host-write throttling, apportion a first address space and a second address space comprising a logical namespace, exempt the second host write stream from host-write throttling when a second available space of memory cells currently available for programming associated with the second address space is greater than zero, and require the second host write stream invalidate logical blocks in an order corresponding to a previous order in which the respective logical blocks were previously programmed.
 2. The apparatus of claim 1, wherein the processor further executes the machine instructions to require the second host write stream program the logical blocks in a sequential order.
 3. (canceled)
 4. The apparatus of claim 1, wherein the processor further executes the machine instructions to require the second host write stream invalidate a previously-programmed logical block address in the second address space before the available space of memory cells currently available for programming associated with the second address space reaches zero.
 5. The apparatus of claim 1, wherein to subject the first host write stream to host-write throttling the processor further executes the machine instructions to determine a first available space of memory cells currently available for programming associated with the first address space, compare the first available space to a predetermined threshold, and reduce a first throughput of the first host write stream based on the first available space not exceeding the threshold, while permitting an unthrottled throughput of the second host write stream.
 6. The apparatus of claim 5, wherein to determine the first available space of memory cells currently available for programming the processor further executes the machine instructions to determine a total available space of memory cells currently available for programming associated with the first address space and the second address space, determine the second available space of memory cells currently available for programming associated with the second address space, and subtract the second available space from the total available space.
 7. The apparatus of claim 1, wherein to exempt the second host write stream from host-write throttling the processor further executes the machine instructions to determine the second available space of memory cells currently available for programming associated with the second address space, and permit an unthrottled throughput of the second host write stream while the second available space is greater than zero.
 8. The apparatus of claim 1, wherein the processor further executes the machine instructions to store the first host write stream in the first address space and store the second host write stream in the second address space.
 9. The apparatus of claim 8, wherein to store the first host write stream in the first address space the processor further executes the machine instructions to combine the first host write stream with a reclamation write stream to form an aggregate write stream, and store the aggregate write stream in the first address space.
 10. The apparatus of claim 1, wherein the processor further executes the machine instructions to reserve an additional quantity of data blocks to the second address space, wherein the additional quantity of data blocks is equal to that over which garbage collection activities are coordinated and is not visible to a host that generates the first host write stream and the second host write stream.
 11. An apparatus for implementing an enhanced-write-bandwidth caching stream, the apparatus comprising: a memory that stores machine instructions; and a processor that executes the machine instructions to divide a stream of host write requests into a first host write stream and a second host write stream comprising latency-sensitive host write requests, define a first address space and a second address space comprising a logical namespace, wherein the first address space corresponds to the first host write stream, and wherein the second address space corresponds to the second host write stream, invalidate logical blocks corresponding to the second host write stream in an order corresponding to a previous order in which the respective logical blocks were previously programmed, and subject the first host write stream to host-write throttling, wherein the second address space is exempted from host-write throttling when a second available space of memory cells currently available for programming associated with the second address space is greater than zero.
 12. The apparatus of claim 11, wherein the processor further executes the machine instructions to program the logical blocks corresponding to the second host write stream in a sequential order.
 13. (canceled)
 14. The apparatus of claim 11, wherein the processor further executes the machine instructions to invalidate a previously-programmed logical block address in the second address space before an available space of memory cells currently available for programming associated with the second address space reaches zero.
 15. A computer-implemented method for implementing an enhanced-write-bandwidth caching stream, the method comprising: apportioning a first address space and a second address space associated with a storage device, the second address space comprising a logical namespace; subjecting the first address space to host-write throttling; exempting the second address space from host-write throttling when a second available space of memory cells currently available for programming associated with the second address space is greater than zero; and requiring logical block addresses corresponding to the second address space be invalidated in an order corresponding to a previous order in which the respective logical blocks were previously programmed.
 16. The method of claim 15, further comprising requiring logical block addresses corresponding to the second address space be programmed in a sequential order.
 17. The method of claim 15, further comprising requiring a previously-programmed logical block address in the second address space be invalidated before an available space of memory cells currently available for programming associated with the second address space reaches zero.
 18. The method of claim 15, further comprising: receiving a first host write stream and a second host write stream comprising latency-sensitive host write requests; storing the first host write stream in the first address space; and storing the second host write stream in the second address space.
 19. The method of claim 18, wherein subjecting the first address space to host-write throttling further comprises: determining a first available space of memory cells currently available for programming associated with the first address space; comparing the first available space to a predetermined threshold; reducing a first throughput of the first host write stream based on the first available space not exceeding the threshold, while permitting an unthrottled throughput of the second host write stream.
 20. The method of claim 19, wherein determining the first available space of memory cells currently available for programming further comprises: determining a total available space of memory cells currently available for programming associated with the first address space and the second address space; determining the second available space of memory cells currently available for programming associated with the second address space; and subtracting the second available space from the total available space. 